The European beaver (Castor fiber Linnaeus, 1758) is an original representative of the European fauna. It became extinct in England as early as in the 13th century. During the 18th and 19th centuries it was hunted to extinction in almost all Europe and did survive only in small colonies on the Rhône River in France, the Elbe River in Germany, in the south of Norway, and in the inflows of the Dnieper River. Thanks to reintroduction at the beginning of the 20th century, stabile populations have developed in Finland, Switzerland, Poland and Austria. The beaver attracted attention of the Slovak scientific community at the time of its return into the landscape of Slovakia after about 120 years. It returned to the country that had been significantly affected by man and raised a new hope that it can contribute to the recovery of the natural environment in relevant areas. The first aim of the work was to find phylogenetic similarities of the northeastern Slovak population with the Ukrainian and Polish ones comparing their adult skulls and mandibles on the basis of craniometric measurements. A total of 28 measurements were taken on each skull and mandible. The statistical evaluation showed that the most similar were the Slovak and Ukrainian skulls, while in 8 cranial parameters the Ukrainian and Polish populations were found to be significantly different. The second aim was related to their incisors. The enamel thickness of Slovak beaver´s incisors in the jaw and mandible were compared to the hare´s incisors. We measured 18 teeth of Castor fiber and 24 of Lepus europaeus, which were previously scanned by the X-Ray Computer Tomography. The results showed that the average thickness of incisors enamel in the mandible was 0,34 mm in C. fiber and 0,120 mm in L. europaeus. On the other hand, the incisors of the maxilla had enamel approximately 0,29 mm thick in C. fiber and 0,097 mm in L. europaeus.